A screening method for a biochar modifier suitable for emission reduction and carbon sequestration of abandoned ion-type rare earth tailing area soil

Abstract

The application discloses a screening method of a biochar modifier suitable for waste ionic rare earth tailing area soil emission reduction and carbon fixation, which comprises the following steps: (1) selecting different biochars, and determining physical and chemical properties of the biochars; (2) performing soil culture test, adding the different biochars into soil by adopting indoor constant-temperature and constant-humidity culture alkali absorption method, and performing soil respiration test determination; (3) calculating soil organic carbon mineralization properties of each group in different culture time sections; and (4) when the soil organic carbon mineralization rate is stable, analyzing the correlation between the soil organic carbon cumulative mineralization amount and the physical and chemical properties of the biochar. The application improves the soil emission reduction and carbon fixation capacity of the waste ionic rare earth tailing area, and also obtains an optimal reference range of the physical and chemical properties of the biochar, thereby providing a theoretical basis for screening the biochar with weak soil organic carbon mineralization in the waste ionic rare earth tailing area. Moreover, the biochar also has a certain effect on the improvement of soil fertility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of soil emission reduction and carbon sequestration, and specifically relates to a screening method of a biochar modifier suitable for soil emission reduction and carbon sequestration in abandoned ionic rare earth tailing area. BACKGROUND

[0002] The abandoned ionic rare earth tailing area is a legacy of rare earth mine operation on the ecological system. The tailings have poor water storage capacity, low content of nitrogen, phosphorus nutrients and organic matter, and high concentration of toxic metals, which causes slow natural plant colonization in the rare earth tailing area, delays the reconstruction of the ecological system structure and function. In addition, the soil structure in the abandoned ionic rare earth tailing area is damaged, soil respiration leads to soil nutrient deficiency, soil infertility and land degradation are increasingly prominent, which restricts agricultural development, and soil respiration exacerbates global warming. Therefore, how to reduce soil carbon emissions in the abandoned ionic rare earth tailing area, improve soil carbon sequestration capacity and promote soil fertility restoration is imminent.

[0003] Biochar is a highly aromatic stable porous carbon-rich substance formed by pyrolysis of organic materials such as agricultural and forestry waste, animal and plant residues, etc. under anaerobic or limited oxygen conditions. Due to its characteristics such as rich pore structure, stable aromatic structure, large specific surface area and a large number of organic functional groups, it is widely used in soil improvement and environmental protection. The study of rice pot experiment by Ruan Zebin et al. found that the addition of biochar increased the soil pH value by 0.23-0.31 units, effectively improving the soil acidic environment. Relevant studies have shown that the addition of biochar to soil increases soil organic carbon content, optimizes soil aeration and water permeability, improves soil aggregate stability, and improves soil microecological environment, which is conducive to the recovery of land productivity. Relevant research has found that biochar made of tobacco stalks, corn stalks, wood branches and rice husks has a significant effect on increasing soil organic carbon, which is conducive to the improvement of soil organic carbon pool. However, biochar has both promoting and inhibiting effects on soil organic carbon mineralization, i.e. positive and negative excitation effects of biochar on soil organic carbon mineralization, which may be related to soil type and biochar properties. After the addition of biochar to soil, various physical and chemical reactions occur over time, which can affect soil organic carbon mineralization through cation-pi interaction, surface complexation, ion exchange and pore blockage adsorption of organic compounds.

[0004] At present, biochar is widely used in farmland ecosystems, but its application in rare earth tailing area soil is relatively less, especially the correlation between biochar characteristic parameters and soil organic carbon mineralization is rarely studied, and the support for the application of biochar in rare earth tailing area is limited. Due to the influence of different soil types, the excitation effect of biochar on soil organic carbon mineralization also varies, so the biochar model applied in farmland ecosystems cannot be directly applied to rare earth tailing area.

[0005] Therefore, how to provide a screening method of a biochar modifier suitable for reducing and fixing carbon in soil in a discarded ion-type rare earth tailing area, provide a theoretical reference range for screening biochar with weak soil organic carbon mineralization in a discarded ion-type rare earth tailing area, and solve the current urgent problem. SUMMARY

[0006] The present application selects three types of biochar (wood carbon, shell carbon and straw carbon) prepared from a total of 10 different raw materials, studies the influence of different types of biochar on soil organic carbon mineralization through laboratory soil culture experiments, analyzes the relationship between biochar characteristic parameters and soil organic carbon mineralization, and determines the key characteristic parameters of biochar affecting soil organic carbon mineralization in a discarded ion-type rare earth tailing area, so as to provide data support for preparing biochar with reduced soil organic carbon mineralization and provide a theoretical basis for screening biochar with weak soil organic carbon mineralization in a discarded ion-type rare earth tailing area.

[0007] The technical scheme of the present application is as follows:

[0008] A screening method of a biochar modifier suitable for reducing and fixing carbon in soil in a discarded ion-type rare earth tailing area, comprising the following steps:

[0009] (1) Randomly select biochar made of different raw materials, measure and analyze the physical and chemical properties of the biochar, and determine the characteristic parameters of the physical and chemical properties;

[0010] (2) Perform soil culture experiments, use indoor constant temperature and humidity culture alkali absorption method, add different biochar to the soil in the discarded ion-type rare earth tailing area at the same proportion and mix well to form a biochar treatment group, and set up a control group without applying biochar, each group is provided with an alkali solution to absorb the carbon dioxide released by soil respiration, and the mass of carbon dioxide absorbed in each group in different culture time sections is measured, that is, the carbon dioxide emission amount of soil respiration in each group is obtained;

[0011] (3) According to the carbon dioxide emission amount of each group obtained in step (2), calculate the soil organic carbon mineralization amount, soil organic carbon mineralization rate, and soil organic carbon cumulative mineralization amount in different culture time sections of each group;

[0012] The specific calculation method is:

[0013] Soil organic carbon mineralization amount = carbon dioxide emission amount of soil respiration / soil dry weight, unit: mg•g -1 ;

[0014] Soil organic carbon mineralization rate = soil organic carbon mineralization amount in different culture time sections / culture time, unit: mg•g -1 •d -1 ;

[0015] The accumulated mineralization amount of soil organic carbon = the sum of the mineralization amounts of soil organic carbon in different time periods, in mg·g -1 ;

[0016] (4) When the soil organic carbon mineralization rate is stable, analyze the correlation between the accumulated mineralization amount of soil organic carbon and the physicochemical properties of the biochar, binomial fitting is performed on the characteristic parameters of the physicochemical properties of the biochar and the accumulated mineralization amount of soil organic carbon respectively, a fitting equation is obtained, and the preferred reference range of the characteristic parameters of the physicochemical properties of the biochar is obtained.

[0017] Further, the biochar made of different raw materials includes at least four of rice husk biochar, apricot shell biochar, coconut shell biochar, walnut shell biochar, reed straw biochar, rice straw biochar, corn straw biochar, corn cob biochar, sawdust biochar, and bamboo biochar.

[0018] Further, the proportion of the different biochar added to the abandoned ion-type rare earth tailings area soil is 5% of the dry weight of the soil.

[0019] Further, in step (2), the soil culture test conditions are 25℃, the soil water content is 60% of the field water holding capacity, and the alkali solution is a 1 mol / L NaOH solution.

[0020] Further, the specific method of step (2) is as follows: 10 different biochars, i.e., rice husk biochar, apricot shell biochar, coconut shell biochar, walnut shell biochar, reed straw biochar, rice straw biochar, corn straw biochar, corn cob biochar, sawdust biochar and bamboo biochar, are added to 450.0 g of abandoned ion-type rare earth tailings area soil at a proportion of 5% respectively and mixed uniformly to form 10 biochar treatment groups, and a soil without biochar application is set as a control group. All the biochar treatment groups and the control group are placed in plastic bottles, and then placed in a closed culture bottle. A plastic bottle containing 10 mL of 1 mol / L NaOH solution and a plastic bottle containing 10 mL of de-carbon dioxide distilled water are also placed in the culture bottle to absorb the carbon dioxide released by soil respiration and maintain the air saturation humidity in the culture bottle. The culture bottle is placed in a 25°C constant temperature incubator, and the soil moisture content is kept at 60% of the field water holding capacity. The plastic bottle containing NaOH is removed at 1, 3, 5, 7, 9, 11, 15, 30 and 60 d of culture respectively, and immediately placed in a newly configured plastic bottle containing 10 mL of 1 mol / L NaOH solution. The NaOH alkali solution that has absorbed carbon dioxide is transferred to a triangular flask, and 5 mL of 1 mol / L barium chloride solution and 2 drops of phenolphthalein indicator are added. The solution is titrated with 0.1 mol / L HCl until the red color disappears, and the mass of absorbed carbon dioxide in each group of alkali solution is calculated by the amount of consumed HCl.

[0021] Further, the characteristic parameters of the physicochemical properties determined in step (1) include pH value, C content and N content, and the fitting equations obtained in step (4) are as follows:

[0022] y1=C1x1 2 +B1x1+A1, wherein A1=139.8160±39.8835, B1=-30.6884±9.0010, C1=1.6955±0.5061, fitting goodness R 2 =0.7417;

[0023] y2=C2x2 2 +B2x2+A2, wherein A2=7.0807±3.4582, B2=-0.2003±0.1132, C2=0.0016±0.0008, fitting goodness R 2 =0.4524;

[0024] y3=C3x3 2 +B3x3+A3, wherein A3=1.7015±0.2981, B3=-2.1185±1.0324, C3=1.3954±0.5579, fitting goodness R 2= 0.6148;

[0025] In the above formula, x1 represents pH value, x2 represents percentage of C content, x3 represents percentage of N content, and y1, y2, y3 all represent values of cumulative mineralization amount of soil organic carbon.

[0026] Further, the preferred reference values of the pH value, C content and N content parameters of the biochar obtained according to the fitting equation are as follows: pH value 9.05, C content 62.59%, and N content 0.76%.

[0027] Further, the characteristic parameters of the physicochemical properties of the biochar determined in step (1) further include hydrophilicity O / C, i.e. the ratio of O content to C content. The hydrophilicity O / C parameter and the cumulative mineralization amount of soil organic carbon are binomially fitted to obtain the fitting equation as follows:

[0028] y4 = C4x4 2 +B4x4+A4, wherein: A4 = 1.9036 ± 0.2104, B4 = -5.5124 ± 1.8425, C4 = 6.9789 ± 2.3814, fitting goodness R 2 = 0.8179;

[0029] In the above formula, x4 represents hydrophilicity O / C, and y4 represents the value of the cumulative mineralization amount of soil organic carbon.

[0030] According to the fitting equation, the preferred reference value of the hydrophilicity O / C parameter of the biochar is 0.39.

[0031] Further, the characteristic parameters of the physicochemical properties of the biochar determined in step (1) further include mesopore volume V meso of the biochar. The mesopore volume V meso parameter and the cumulative mineralization amount of soil organic carbon are binomially fitted to obtain the fitting equation as follows:

[0032] y5 = C5x5 2 +B5x5+A5, wherein: A5 = 3.2333 ± 1.6020, B5 = -79.4511 ± 85.3912, C5 = 656.2212 ± 801.9481, fitting goodness R 2 = 0.5348;

[0033] In the above formula, x5 represents the value of the mesopore volume V meso of the biochar, and y5 represents the value of the cumulative mineralization amount of soil organic carbon.

[0034] According to the fitting equation, the preferred reference value of the mesopore volume parameter of the biochar is 0.06 mm 3 / g.

[0035] Further, the characteristic parameters of the biochar physicochemical properties determined in step (1) further include the number of surface functional groups in the infrared spectrum, and the number of surface functional groups is binomially fitted with the cumulative mineralization amount of soil organic carbon to obtain a fitting equation as follows:

[0036] y6=C6x6 2 +B6x6+A6, wherein: A6=7.0200±1.2308, B6=-2.5533±0.6782, C6=0.2467±0.0723, the goodness of fit R 2 =0.9537;

[0037] In the above formula, x6 represents the number of surface functional groups, and y6 represents the numerical value of the cumulative mineralization amount of soil organic carbon.

[0038] According to the fitting equation, the preferred reference value of the number of surface functional groups of the biochar is 5.

[0039] The beneficial effects of the present application are:

[0040] 1. The present application analyzes the physicochemical properties of biochar, and adds 10 different types of biochar (rice husk biochar, apricot shell biochar, coconut shell biochar, walnut shell biochar, reed straw biochar, rice straw biochar, corn straw biochar, corn cob biochar, sawdust biochar, and bamboo biochar) to the abandoned ion-type rare earth tailings area soil for soil culture test, analyzes the relationship between the characteristic parameters (pH value, C content and N content) of the physicochemical properties of biochar and the soil organic carbon mineralization characteristics, and selects the preferred reference value of the characteristic parameters of the physicochemical properties of biochar (biochar pH value is 9.05, C content is 62.59%, and N content is 0.76%), which provides a basis for selecting suitable pH value, C content and N content of biochar for soil emission reduction and carbon sequestration in abandoned ion-type rare earth tailings area.

[0041] 2. The relationship between the priming effect of 10 different types of biochar on soil organic carbon mineralization and the physicochemical properties of biochar is studied, and the results show that the addition of 10 types of biochar promotes the mineralization of soil organic carbon in the abandoned ion-type rare earth tailings area, i.e. there is a positive priming effect, and the positive priming effect of corn cob biochar is the weakest, which has certain significance in reducing the mineralization of soil organic carbon in the abandoned ion-type rare earth tailings area.

[0042] 3. In order to explore the correlation between the hydrophilicity O / C (i.e. the ratio of O content to C content) of biochar and the mineralization characteristics of soil organic carbon, five different types of biochar (coconut shell biochar, rice straw biochar, corn cob biochar, apricot shell biochar and bamboo biochar) are added to the soil of abandoned ion-type rare earth tailings area for soil culture test, the relationship between the hydrophilicity O / C parameter of biochar and the mineralization characteristics of soil organic carbon is analyzed, and the optimal reference value 0.39 of the hydrophilicity O / C parameter is selected, which provides a basis for selecting suitable hydrophilicity O / C biochar for soil emission reduction and carbon sequestration in abandoned ion-type rare earth tailings area.

[0043] 4. In order to explore the correlation between the pore structure of biochar and the mineralization characteristics of soil organic carbon, four different types of biochar (apricot shell biochar, coconut shell biochar, corn cob biochar and wood chip biochar) are added to the soil of abandoned ion-type rare earth tailings area for soil culture test, the relationship between the characteristic parameters (mesopore volume V meso ) of the physicochemical properties of biochar and the mineralization characteristics of soil organic carbon is analyzed, and the optimal reference value 0.06 mm meso / g of the mesopore volume V 3 parameter of biochar is selected, which provides a basis for selecting suitable pore structure biochar for soil emission reduction and carbon sequestration in abandoned ion-type rare earth tailings area.

[0044] 5. In order to explore the correlation between the number of surface groups of biochar infrared spectrum and the mineralization characteristics of soil organic carbon, five different types of biochar (coconut shell biochar, rice straw biochar, corn cob biochar, wood chip biochar and bamboo biochar) are added to the soil of abandoned ion-type rare earth tailings area for soil culture test, the relationship between the characteristic parameters (number of surface groups) of the physicochemical properties of biochar and the mineralization characteristics of soil organic carbon is analyzed, and the optimal reference value 5 of the number of surface groups parameter of biochar is selected, which provides a basis for selecting suitable number of surface functional groups biochar for soil emission reduction and carbon sequestration in abandoned ion-type rare earth tailings area.

[0045] 6. The present application can more comprehensively obtain the correlation between the physicochemical properties of biochar and the mineralization characteristics of soil organic carbon from the analysis of multiple dimensions (pH value, element content, pore structure and infrared spectrum characteristics) of the physicochemical properties of biochar. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is a schematic diagram of the soil culture test of the present application;

[0047] Figure 2 It is the N2 adsorption-desorption isotherm obtained by BET specific surface area test of different biochar;

[0048] Figure 3 It is the pore size distribution curve of different biochar;

[0049] Figure 4 Infrared spectra of different biochar;

[0050] Figure 5 Soil organic carbon mineralization rate of different biochar treatment;

[0051] Figure 6 Effect of different biochar treatment on priming effect of soil organic carbon;

[0052] Figure 7 Binomial fitting curve of pH value of different biochar and cumulative mineralization amount of soil organic carbon;

[0053] Figure 8 Binomial fitting curve of C content of different biochar and cumulative mineralization amount of soil organic carbon;

[0054] Figure 9 Binomial fitting curve of N content of different biochar and cumulative mineralization amount of soil organic carbon;

[0055] Figure 10 Binomial fitting curve of hydrophilic O / C parameter of different biochar and cumulative mineralization amount of soil organic carbon;

[0056] Figure 11 Binomial fitting curve of mesopore volume V meso Parameter of different biochar and cumulative mineralization amount of soil organic carbon;

[0057] Figure 12 Binomial fitting curve of surface group number parameter of different biochar and cumulative mineralization amount of soil organic carbon. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0059] I. Test materials

[0060] The soil sample was taken from the surface soil of 0-20 cm in a rare earth tailing area (N24°58′45″, E115°3′18″, elevation 419.88 m) in Dingnan County, Ganzhou City, Jiangxi Province. The stones, roots and the like in the soil were removed, and the soil was naturally dried, passed through a 2 mm sieve, mixed and uniformly preserved for standby. The physical and chemical properties of the test soil are shown in Table 1.

[0061] Table 1 Physical and chemical properties of the test soil

[0062]

[0063] Biochar was produced by Henan Lizze Environmental Protection Technology Co., Ltd. and sieved to 2 mm for use. Production process: raw materials were dried and crushed, and then pyrolyzed at about 500 ℃, with a heating rate of 10 ℃·min -1 and stable carbonization for 2-3 h.

[0064] II. Analysis method

[0065] The determination method of soil samples: the pH value was determined by glass electrode method with a soil-water ratio of 1:5 (w / v); the organic matter was determined by potassium dichromate volumetric method-dilution heat method; the alkali-hydrolyzable nitrogen was determined by alkali-hydrolyzable diffusion method; the available phosphorus was determined by sodium bicarbonate extraction molybdenum-antimony anti-colorimetric method; the available potassium was determined by ammonium acetate extraction flame photometry; and the total nitrogen was determined by semi-micro Kjeldahl method.

[0066] The determination method of biochar characteristic parameters: the pH value was determined by glass electrode method with a biochar-water ratio of 1:20 (m / v); the C, N and O element contents were determined by CHNS element analyzer; the BET specific surface area and pore size were determined by specific surface area and pore size analyzer; and the surface functional groups were determined by potassium bromide powder tablet-Fourier infrared spectroscopy method.

[0067] III. Test method

[0068] For example Figure 1The experiment was conducted in a constant temperature and humidity indoor culture alkali absorption method, and 11 treatments were set up, with 4 replicates in each treatment. Ten different sources of biochar (rice husk biochar DK, apricot kernel biochar XK, coconut shell biochar YK, walnut shell biochar HK, reed straw biochar LJ, rice straw biochar SD, corn straw biochar YJ, corn cob biochar YX, sawdust biochar MB, and bamboo biochar ZB) were added to 450.0 g of soil at a ratio of 5% (w / w, based on dry soil) and mixed evenly to form 10 biochar treatment groups. Another group of soil without biochar application was set up as the control group CK. All biochar treatment groups and the control group CK were placed in plastic bottles and then put into airtight culture bottles. A plastic bottle containing 10 mL of 1 mol / L NaOH solution and another plastic bottle containing 10 mL of de-carbon dioxide distilled water were also placed in the culture bottles to absorb the carbon dioxide released by soil respiration and maintain the air saturation humidity in the culture bottles, respectively. The culture bottles were placed in a 25°C constant temperature incubator, and the soil moisture content was maintained at 60% of the field water holding capacity. The plastic bottles containing NaOH were removed on the 1st, 3rd, 5th, 7th, 9th, 11th, 15th, 30th, and 60th days of culture, and immediately placed into a newly configured plastic bottle containing 10 mL of 1 mol / L NaOH solution. The NaOH alkali solution that had absorbed carbon dioxide was transferred to a triangular flask, and 5 mL of 1 mol / L barium chloride solution and 2 drops of phenolphthalein indicator were added. The solution was titrated with 0.1 mol / L HCl until the red color disappeared. The mass of carbon dioxide absorbed in each group of alkali solution during different culture time periods was calculated, and the carbon dioxide emissions of each group of soil respiration were obtained.

[0069] IV. Results and analysis

[0070] 1. Physicochemical properties of biochar

[0071] (1) pH value, C content, and N content

[0072] Table 2

[0073] Biochar type pH C（%） N（%） MB 8.07 90.49 1.72 SD 8.4 88.85 1.69 YK 9.65 89.15 0.12 HK 8.7 88.16 0.15 ZB 9.42 42.19 0.19 DK 9.36 43.88 0.41 XK 9.58 82.72 0.24 LJ 9.24 46.66 1.46 YJ 9.39 53.24 1.13 YX 8.44 75.3 0.6

[0074] (2) Hydrophilic O / C

[0075] Table 3

[0076] Biochar type C（%） O（%） O / C SD 88.85 5.87 0.066 YK 89.15 8.92 0.100 ZB 42.19 27.9 0.661 XK 82.72 15.79 0.191 YX 75.3 14.2 0.189

[0077] (3) Pore structure - mesopore volume V meso

[0078] The BET specific surface area and pore structure of four different types of biochar (coconut shell biochar YK, corn cob biochar YX, sawdust biochar MB and apricot shell biochar ZB) are tested, and the N2 adsorption-desorption isotherm of the four biochar samples is obtained Figure 2 , and the pore size distribution curve is Figure 3 .

[0079] According to the method of national standard GB / T 21650.2-2008 "Mercury intrusion porosimetry and gas adsorption method for determining pore size distribution and porosity of solid materials Part 2: Gas adsorption method for analyzing mesopores and macropores", the mesopore volume V meso The results are shown in the following table 4.

[0080] Table 4

[0081] Biochar type V meso (mm 3 / g)]]> MB 0.012 YK 0.023 XK 0.065 YX 0.094

[0082] (4) Infrared spectrum characteristics

[0083] The infrared spectrum of five different types of biochar (coconut shell biochar YK, rice straw biochar SD, corn cob biochar YX, sawdust biochar MB and bamboo biochar ZB) is determined, and the specific infrared spectrum is shown in Figure 4 .

[0084] Figure 4 cm -1 from the hydroxyl (-OH) stretching peak, 2809 cm -1 and 2721 cm -1 are asymmetric and symmetric stretching vibration peaks of aliphatic CH2, 1598 cm -1 is the C=O stretching vibration absorption peak of carboxylic acid, 1382 cm -1 and 1349 cm -1 are the absorption peaks of aromatic C=C vibration in lignin, 1078 cm -1 is the C-O vibration absorption peak of cellulose or hemicellulose, 765 cm -1 is the aromatic C-H absorption peak.

[0085] The surface functional group quantity results of the five types of biochar are shown in the following table 5.

[0086] Table 5

[0087] Biochar type Number of surface functional groups MB 2 SD 3 YK 7 ZB 7 YX 7

[0088] 2, Soil organic carbon mineralization characteristics of different biochar treatment groups

[0089] The mass of carbon dioxide absorbed in each group of alkali solution, i.e. the emission of carbon dioxide, was obtained according to the above experiment, and the mineralization characteristics of soil organic carbon were calculated according to the following formula:

[0090] The mineralization amount of soil organic carbon = the emission amount of carbon dioxide of soil respiration / the dry weight of soil, in mg•g -1 ;

[0091] The mineralization rate of soil organic carbon = the mineralization amount of soil organic carbon in different incubation time sections / incubation time, in mg•g -1 •d -1 ;

[0092] The cumulative mineralization amount of soil organic carbon = the cumulative sum of the mineralization amount of soil organic carbon in different time sections, in mg•g -1 ;

[0093] The average mineralization rate of soil organic carbon = the cumulative mineralization amount of soil organic carbon / total incubation time, in mg•g -1 •d -1 ;

[0094] The cumulative priming effect of biochar = the cumulative mineralization amount of soil organic carbon of the soil added with biochar - the cumulative mineralization amount of soil organic carbon of the control group, in mg•g -1 .

[0095] (1) Influence of different biochars on the mineralization rate of soil organic carbon

[0096] The results of the mineralization rate of soil organic carbon after treatment with different biochars are shown in Figure 5 . With the passage of time, the trends of the mineralization rate of soil organic carbon of each treatment were basically consistent. Within 15 d before incubation, the mineralization rate of soil organic carbon of each treatment decreased sharply, and after 15 d, the mineralization rate of soil organic carbon gradually stabilized. On the first day of incubation, the mineralization rate of soil organic carbon was the strongest, and the soil respiration was relatively intense. The mineralization rate of soil organic carbon of the MB treatment was the strongest, 0.407 mg•g -1 •d -1 , which was significantly higher than that of other treatments. The mineralization rate of soil organic carbon of the CK treatment was the weakest, 0.053 mg•g -1 •d -1 , which was not significantly different from that of the YX treatment (0.055 mg•g -1 •d -1 ). It can be seen that the addition of biochar promotes the mineralization of soil organic carbon, and the mineralization rate of soil organic carbon tends to stabilize after 15 d of addition. The YX treatment has the weakest promoting effect on the mineralization rate of soil organic carbon, and does not significantly promote the mineralization of soil organic carbon.

[0097] (2) Effects of different biochar on the cumulative mineralization of soil organic carbon

[0098] The data of CO2 emission, average mineralization rate of soil organic carbon, and cumulative mineralization of soil organic carbon of each group treated with different biochar are shown in Table 6.

[0099] Table 6 Mineralization characteristics of soil organic carbon of each group

[0100]

[0101] Note: The data in the table were analyzed by SPSS (LSD method, significant level 0.05), wherein, the same column with different superscripts indicated significant difference (P<0.05) between treatment groups, and the same column with the same superscript indicated no significant difference (P>0.05) between treatment groups.

[0102] As shown in Table 6, the addition of biochar promoted the emission of soil CO2 and increased the mineralization of soil organic carbon. Among them, the soil organic carbon mineralization effect of MB treatment was the most obvious, which was significantly higher than that of other biochar treatments, and the average mineralization rate of soil organic carbon, the cumulative mineralization of soil organic carbon, and the cumulative release of soil CO2 were the highest, about 3 times of CK. The soil organic carbon mineralization of YX treatment was the weakest, and there was no significant difference in the average mineralization rate of soil organic carbon, the cumulative mineralization of soil organic carbon, and the cumulative release of soil CO2 compared with CK.

[0103] Therefore, the addition of biochar had a promoting effect on soil organic carbon mineralization during the incubation period, and YX treatment had the weakest effect on promoting soil organic carbon mineralization, which had no significant difference with CK treatment.

[0104] (3) Effects of biochar on priming effect of soil organic carbon

[0105] As shown in Figure 6 (a), under the condition of biochar treatment, the trend of soil organic carbon priming effect rate with time was basically the same, and the soil organic carbon priming effect rate gradually decreased within 15 d before incubation, and then gradually stabilized after 15 d. During the incubation period, the priming effect rate of MB treatment was the fastest, with an average priming effect rate of 0.032 mg•g -1 •d -1 , the priming effect rate of YX treatment was the slowest, with an average priming effect rate of 0.0004 mg•g -1 •d -1 , and the priming effect rate of MB treatment was significantly higher than that of other treatments. As shown in Figure 6(b) It can be seen that the cumulative priming effect of biochar gradually increased with the extension of incubation time, which showed a trend of first fast, then slow and finally stable. The growth rate of biochar priming effect decreased gradually in the first 15 days, and remained stable in the last 15 days. Among them, the growth rate of biochar priming effect of MB treatment remained basically unchanged after 15 days, which increased at a rate of 0.0178 mg•g -1 •d -1 , which was significantly higher than that of other treatments, while the growth rate of biochar priming effect of YX treatment was the lowest, which was 0.0001 mg•g -1 •d -1 . Therefore, the priming effect of biochar on soil organic carbon was basically stable after 15 days of soil application, and the positive priming effect of MB treatment was the strongest, while the positive priming effect of YX treatment was the weakest.

[0106] 3. Screening of physicochemical properties of biochar

[0107] (1) pH value, C content, N content

[0108] The pH value, C content and N content of 10 different biochars obtained in Table 2 were binomially fitted with the cumulative mineralization amount of soil organic carbon obtained in Table 6, respectively, and it can be seen that the pH value, C content and N content of biochar and the cumulative mineralization amount of soil organic carbon meet the binomial distribution. Figure 7-9

[0109] The binomial fitting equations are as follows:

[0110] y1=C1x1 2 +B1x1+A1, wherein A1=139.8160±39.8835, B1=-30.6884±9.0010, C1=1.6955±0.5061, the goodness of fit R 2 =0.7417;

[0111] y2=C2x2 2 +B2x2+A2, wherein A2=7.0807±3.4582, B2=-0.2003±0.1132, C2=0.0016±0.0008, the goodness of fit R 2 =0.4524;

[0112] y3=C3x3 2 +B3x3+A3, wherein A3=1.7015±0.2981, B3=-2.1185±1.0324, C3=1.3954±0.5579, the goodness of fit R 2 =0.6148;

[0113] ​In the above formula, x1 represents pH value, x2 represents percentage of C content, x3 represents percentage of N content, and y1, y2, and y3 all represent the value of cumulative mineralization amount of soil organic carbon.

[0114] According to the calculation of the binomial fitting curve result, when the pH value of the biochar is 9.05, the C content is 62.59%, and the N content is 0.76%, the cumulative mineralization amount of soil organic carbon can be at the lowest level. Therefore, the suitable pH, C content, and N content of the biochar have a good effect on reducing the mineralization of soil organic carbon.

[0115] (2) Hydrophilic O / C

[0116] The hydrophilic O / C parameters of the five different biochars obtained from Table 3 were binomially fitted with the cumulative mineralization amount of soil organic carbon obtained from Table 6, respectively, and the binomial fitting equation was: Figure 10 It can be known that the hydrophilic O / C parameter of the biochar meets the binomial distribution with the cumulative mineralization amount of soil organic carbon.

[0117] The binomial fitting equation is:

[0118] y4=C4x4 2 +B4x4+A4, wherein: A4=1.9036±0.2104, B4=-5.5124±1.8425, C4=6.9789±2.3814, the goodness of fit R 2 =0.8179;

[0119] In the above formula, x4 represents the hydrophilic O / C, and y4 represents the value of the cumulative mineralization amount of soil organic carbon.

[0120] According to the calculation of the binomial fitting curve result, when the O / C of the biochar is 0.39, the cumulative mineralization amount of soil organic carbon can be at the lowest level. Therefore, the suitable hydrophilicity of the biochar has a good effect on reducing the mineralization of soil organic carbon.

[0121] (3) Mesopore volume V meso

[0122] The mesopore volume V meso parameters of the four different biochars obtained from Table 4 were binomially fitted with the cumulative mineralization amount of soil organic carbon obtained from Table 6, respectively, and the binomial fitting equation was: Figure 11 It can be known that the mesopore volume V meso parameter of the biochar meets the binomial distribution with the cumulative mineralization amount of soil organic carbon.

[0123] The binomial fitting equation is:

[0124] y5=C5x5 2+B5x5+A5, wherein: A5 = 3.2333 ± 1.6020, B5 = -79.4511 ± 85.3912, C5 = 656.2212 ± 801.9481, goodness of fit R 2 = 0.5348.

[0125] In the above formula, x5 represents the value of mesopore volume V meso , and y5 represents the value of cumulative mineralization amount of soil organic carbon.

[0126] According to the binomial fitting curve result calculation, when the mesopore volume V meso of the biochar is 0.06 mm 3 / g, the cumulative mineralization amount of soil organic carbon can be at the lowest level. Therefore, the suitable mesopore volume V meso of the biochar has a good effect on reducing the mineralization of soil organic carbon.

[0127] (4) Number of surface functional groups

[0128] The number of surface functional groups of the five different biochars obtained in Table 5 is respectively binomially fitted with the cumulative mineralization amount of soil organic carbon obtained in Table 6, and it can be known that the number of surface functional groups of the biochar and the cumulative mineralization amount of soil organic carbon satisfy binomial distribution. Figure 12

[0129] The binomial fitting equation is:

[0130] y6 = C6x6 2 +B6x6+A6, wherein: A6 = 7.0200 ± 1.2308, B6 = -2.5533 ± 0.6782, C6 = 0.2467 ± 0.0723, goodness of fit R 2 = 0.9537.

[0131] In the above formula, x6 represents the number of surface functional groups, and y6 represents the value of cumulative mineralization amount of soil organic carbon.

[0132] According to the fitting equation, the preferred reference value of the number of surface functional groups of the biochar is 5.

[0133] According to the binomial fitting curve result calculation, when the number of surface functional groups of the biochar is 5, the cumulative mineralization amount of soil organic carbon can be at the lowest level. Therefore, the suitable number of surface functional groups of the biochar has a good effect on reducing the mineralization of soil organic carbon.​

Claims

1. A screening method for a biochar amendment suitable for carbon sequestration and emission reduction of soil in a waste ionic rare earth tailing area, characterized in that: The method comprises the following steps: (1) randomly selecting biochar made of different raw materials, determining and analyzing the physicochemical properties of the biochar, and determining the characteristic parameters of the physicochemical properties, wherein the determined characteristic parameters of the physicochemical properties include pH value, C content, N content and hydrophilic O / C; (2) performing a soil culture test, using an indoor constant temperature and humidity culture alkali absorption method, adding different biochar to abandoned ion-type rare earth tailing area soil in the same proportion and mixing uniformly to form a biochar treatment group, and setting up a soil control group without applying biochar, setting up alkali for each group to absorb carbon dioxide released by soil respiration, and respectively determining the mass of carbon dioxide absorbed in the alkali of each group in different culture time periods, i.e. the carbon dioxide emission amount of soil respiration of each group; (3) calculating the soil organic carbon mineralization amount, soil organic carbon mineralization rate and soil organic carbon cumulative mineralization amount of each group in different culture time periods according to the carbon dioxide emission amount of each group obtained in step (2); (4) when the soil organic carbon mineralization rate is stable, analyzing the correlation between the soil organic carbon cumulative mineralization amount and the physicochemical properties of the biochar, performing binomial fitting of the characteristic parameters of the physicochemical properties of each group of biochar and the soil organic carbon cumulative mineralization amount, obtaining a fitting equation, and obtaining an optimized reference range of the characteristic parameters of the physicochemical properties of the biochar.

2. The screening method according to claim 1, characterized in that: The biochar made of different raw materials includes at least four of rice husk biochar, apricot shell biochar, coconut shell biochar, walnut shell biochar, reed straw biochar, rice straw biochar, corn straw biochar, corn cob biochar, sawdust biochar and bamboo biochar.

3. The screening method according to claim 1, characterized in that: The proportion of the different biochar added to the abandoned ion-type rare earth tailing area soil is 5% of the dry weight of the soil.

4. The screening method of claim 1, wherein: In step (2), the conditions of the soil culture test are 25 DEG C, and the soil moisture content is 60% of the field capacity, and the alkali is 1 mol / L NaOH solution.

5. The screening method of claim 1, wherein: The specific method of the soil culture test of step (2) is as follows: 10 different kinds of biochar, i.e. rice husk biochar, apricot shell biochar, coconut shell biochar, walnut shell biochar, reed straw biochar, rice straw biochar, corn straw biochar, corn cob biochar, sawdust biochar and bamboo biochar, are added into 450.0 g of abandoned ion-type rare earth tailings area soil at a proportion of 5% respectively and mixed uniformly to form 10 groups of biochar treatment groups, and a soil without biochar application is set as a control group. All the biochar treatment groups and the control group are placed in plastic bottles and then in a closed culture bottle. A plastic bottle containing 10 mL of 1 mol / L NaOH solution and a plastic bottle containing 10 mL of de-carbon dioxide distilled water are also placed in the culture bottle to absorb the carbon dioxide released by soil respiration and maintain the air saturation humidity in the culture bottle respectively. The culture bottle is placed in a 25 ℃ constant temperature incubator, and the soil moisture content is kept at 60% of the field water holding capacity. The plastic bottle containing NaOH is removed on the 1st, 3rd, 5th, 7th, 9th, 11th, 15th, 30th and 60th day of culture respectively, and immediately placed in a newly configured plastic bottle containing 10 mL of 1 mol / L NaOH solution. The NaOH alkali solution that has absorbed carbon dioxide is completely transferred into a triangular flask, and 5 mL of 1 mol / L barium chloride solution and 2 drops of phenolphthalein indicator are added. The solution is titrated with 0.1 mol / L HCl until the red color disappears, and the mass of carbon dioxide absorbed in each group of alkali solution is calculated by the amount of HCl consumed.

6. The screening method of claim 1, wherein: For the characteristic parameters of the physicochemical properties determined in step (1), i.e. pH value, C content and N content, the fitting equations obtained in step (4) are as follows: y1 = C1x1 2 + B1x1 + A1, where: A1 = 139.8160 ± 39.8835, B1 = -30.6884 ± 9.0010, C1 = 1.6955 ± 0.5061, goodness of fit R 2 = 0.7417; y2 = C2x2 2 + B2x2 + A2, where: A2 = 7.0807 ± 3.4582, B2 = -0.2003 ± 0.1132, C2 = 0.0016 ± 0.0008, goodness of fit R 2 = 0.4524; y3 = C3x3 2 + B3x3 + A3, where: A3 = 1.7015 ± 0.2981, B3 = -2.1185 ± 1.0324, C3 = 1.3954 ± 0.5579, goodness of fit R 2 = 0.6148; In the above equations, x1 represents the pH value, x2 represents the percentage of C content, x3 represents the percentage of N content, and y1, y2 and y3 all represent the numerical value of the cumulative mineralization amount of soil organic carbon.

7. The screening method according to claim 6, characterized in that: According to the fitting equations, the optimal reference values of the pH value, C content and N content parameters of biochar are as follows: pH value 9.05, C content 62.59% and N content 0.76%.

8. The screening method according to any one of claims 1 to 6, characterized in that: For the characteristic parameter of the physicochemical properties of biochar determined in step (1), i.e. hydrophilicity O / C, i.e. the ratio of O content to C content, the hydrophilicity O / C parameter is binomially fitted with the cumulative mineralization amount of soil organic carbon to obtain the fitting equation as follows: y4 = C4x4 2 + B4x4 + A4, where: A4 = 1.9036 ± 0.2104, B4 = -5.5124 ± 1.8425, C4 = 6.9789 ± 2.3814, goodness of fit R 2 = 0.8179; In the above equation, x4 represents the hydrophilicity O / C, and y4 represents the numerical value of the cumulative mineralization amount of soil organic carbon. According to the fitting equation, the optimal reference value of the hydrophilicity O / C parameter of biochar is 0.

39.

9. The screening method according to any one of claims 1 to 6, characterized in that: The characteristic parameters of the physicochemical properties of the biochar determined in step (1) further include mesopore volume V meso The mesopore volume V meso The binomial fitting of the parameter and the accumulated mineralization amount of soil organic carbon is as follows: y5 = C5x5 2 + B5x5 + A5, where: A5 = 3.2333 ± 1.6020, B5 = -79.4511 ± 85.3912, C5 = 656.2212 ± 801.9481, goodness of fit R 2 = 0.5348; In the above formula, x5 represents the value of mesopore volume V meso of soil organic carbon accumulation mineralization, and y5 represents the value of soil organic carbon accumulation mineralization. According to the fitting equation, the preferred reference value of the mesopore volume parameter of the biochar is 0.06 mm 3 / g.

10. The screening method according to any one of claims 1 to 6, characterized in that: The characteristic parameters of the physicochemical properties of biochar determined in step (1) also include the number of surface functional groups in the infrared spectrum. The number of surface functional groups parameter is binomially fitted with the cumulative mineralization amount of soil organic carbon to obtain the fitting equation as follows: y6 = C6x6 2 + B6x6+ A6, where: A6= 7.0200 ± 1.2308, B6= -2.5533 ± 0.6782, C6= 0.2467 ± 0.0723, goodness of fit R 2 = 0.9537; In the above equation, x6 represents the number of surface functional groups, and y6 represents the numerical value of the cumulative mineralization amount of soil organic carbon. According to the fitting equation, the optimal reference value of the number of surface functional groups parameter of biochar is 5.

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